Update README with rpi-update recommendation
Update README with rpi-update recommendation

firepick/FireHawk,malsony/raspbian-ua-netinst,dicer/raspbian-ua-netinst,FooDeas/raspberrypi-ua-netinst,bbinet/raspbian-ua-netinst,beylsp/rpi-installer,Zspark23/raspbian-ua-netinst-1,jturner314/raspbian-ua-netinst,Zspark23/raspbian-ua-netinst,matt2005/raspbian-ua-netinst,Zspark23/raspbian-ua-netinst-1,daytonpid/FireHawk,cybercircuits/raspbian-ua-netinst,kolargol/raspbian-ua-netinst,beylsp/rpi-installer,Zeerix/raspbian-ua-netinst,yodaaut/raspbian-ua-netinst,racing-tech/rrp-raspi-installer,racing-tech/rrp-raspi-installer,krazedkrish/Web-Pro-ua-netinst,Zspark23/raspbian-ua-netinst-1